KR20130018247A - Lanthanum hexaboride sintered body, target and lanthanum hexaboride film each comprising same, and process for production of the sintered body - Google Patents

Abstract

The main component is lanthanum hexaboride, and the nitrogen element content is 0.1% by mass or more and 3% by mass or less, and the content of impurities composed of carbon alone and / or at least two elements selected from La, C, O, and B is 0.3. LaB ₆ having a high purity, high density, excellent crystallinity and good work function by using a lanthanum hexafluoroborate sintered body having a relative density of 88% or more and a target made of the lanthanum hexafluoroborate sintered body by volume% or less. LaB ₆ suitable for sputtering targets giving thin films A sintered compact can be provided.

Description

LANTHANUM HEXABORIDE SINTERED BODY, TARGET AND LANTHANUM HEXABORIDE FILM EACH COMPRISING SAME, AND PROCESS FOR PRODUCTION OF THE SINTERED BODY}

The present invention relates to a lanthanum hexaboride (LaB ₆ ) sintered body, a target using the same, a lanthanum hexahexaborate film, and a method for producing the LaB ₆ sintered body. More specifically, the present invention is a LaB ₆ sintered body suitable as a sputtering target for producing a LaB ₆ thin film, which is high purity, dense, excellent in crystallinity and good in work function, a target formed using the same, and a film forming using the target. And (iii) a lanthanum hexaboride film and an effective method for producing the LaB ₆ sintered body.

Since metal borides are chemically stable and exhibit various electrical properties depending on the content of boron, various application developments are expected. Among them, in particular, lanthanum hexahexaborate (LaB ₆ ) has a small work function, and thus development of its use as an electrode material is being progressed by electron emission devices, lighting and the like. In addition, the said work function means the minimum energy required to take out an electron from the surface of a material. The smaller the work function of the electron emitting device is, the more preferable.

The LaB ₆ is often used as a thin film. Various methods are examined for the film forming method of the LaB ₆ thin film. Among these methods, the sputtering method is used are suitable with the LaB ₆ film formation target to a dense film. It is necessary for the LaB ₆ thin film to have a small work function, and for that purpose, a film of high purity and high crystallinity is required.

In general, the target is required to be dense and of high purity. Conventional LaB ₆ targets have been prepared by sintering commercially available LaB ₆ powder.

However, commercially available LaB ₆ powder contains 1.5 mass% or more of lanthanum oxide, boron oxide, and lanthanum-boron complex oxide as oxygen, and 0.2 mass% or more of lanthanum carbide and boron carbide in terms of carbon.

Lanthanum oxide and boron oxide contained in the LaB ₆ commercially available powder is mainly LaB ₆ is oxidized by oxygen in atmosphere. The LaB ₆ industrial production of a commercially available powder process, the handling of the blocks, a completely air because it requires a process of grinding with a suitable particle size for the composite powder as a sintered material, it is not practical. The fracture surface portion newly produced by this pulverization reacts with oxygen in the atmosphere to form lanthanum oxide and boron oxide.

In addition, the lanthanum contained in the LaB ₆ commercially available powder-boron complex oxide, is a LaB to the synthesis of _six commercially available powder, contained in the lanthanum oxide and the B material included in the various La raw material boron oxide are reacted to produce that.

On the other hand, lanthanum carbide and boron carbide are produced due to the carbon added at the time of synthesis. The said carbon is added in order to reduce | restore to the metal La state which can react with B from various La raw materials at the time of synthesis | combination. Usually, since carbon is added excessively in order to fully react La, remaining carbon reacts with La and B, and it becomes lanthanum carbide and boron carbide. It is not practical to avoid the production of these carbides. Therefore, LaB ₆ in the commercially available powder produced by the industrial production method, lanthanum oxide, boron oxide, lanthanum - it is very difficult to avoid that the boron compound oxide, lanthanum carbide, boron carbide, or carbon-containing residue.

Impurities contained in these LaB ₆ powders cannot be removed even when heated to the sintering temperature, and remain at the grain boundaries of the LaB ₆ sintered body. Therefore, the developed LaB ₆ sintered compact manufactured using commercially available LaB ₆ powder contains at least 3 volume% of impurities derived from the raw material powder. In addition, impurities contained in the target are introduced into the sputtered film as they are. In the impurities, because the work function greater than the LaB _6, LaB ₆ film that contains such impurities, the greater the work function.

Therefore, when the conventional LaB ₆ target manufactured by sintering LaB ₆ commercial powder is used, the LaB ₆ film obtained has a problem that the impurity content increases, and as a result, the work function of the film increases.

In order to reduce the impurity content in the target, a method of sintering LaB ₆ powder having high purity is effective. Containing impurities in LaB ₆ powder can be effectively removed by heating and washing in an inorganic acid. By using the target highly purified by the above acid washing, a LaB ₆ film having a low impurity content can be formed.

On the other hand, application of the LaB ₆ thin film to an electron emission device, an electrode material, and the like has been studied. Film-forming substrate (基板) of the LaB _6, the thin film is used such as a week, a metal substrate, a glass substrate, a Si wafer. When the highly purified LaB ₆ sintered compact was applied to these targets and formed into a film, the obtained film had high purity but poor crystallinity, easy peeling off of the film, and high work function.

In general, when a film having a composition or crystal structure different from that of a film forming substrate is formed by sputtering, an internal stress is generated in the sputtered film due to a difference in physical properties of the film and the film, resulting in poor crystallinity of the film.

This phenomenon also occurs in the LaB ₆ sputtered film and depends on the material of the substrate, and this tendency is remarkable when a substrate having a significantly different thermal expansion coefficient and lattice constant is used compared to LaB ₆ . A large internal stress of the film deteriorates the crystallinity of the LaB ₆ film. It is known that there is a relationship between the crystallinity and the work function of the film, and the decrease in the crystallinity leads to an increase in the work function. Furthermore, when the internal stress of the film is large, the film is likely to peel off from the substrate, so that the film cannot be formed.

If the LaB ₆ sputtered film contains impurities that can alleviate the thermal expansion coefficient and lattice constant difference between LaB ₆ and the substrate, the internal stress of the film can be reduced.

However, these impurities have a larger work function than LaB ₆ . For this reason, if the LaB ₆ film contains impurities, the internal stress of the film is relaxed, but the work function cannot be increased.

Therefore, there is a demand for a target material capable of producing a LaB ₆ sputtered film having high adhesion and crystallinity, in which impurities which increase the work function are not contained and the thermal expansion difference between LaB ₆ and the substrate is reduced.

On the other hand, since LaB ₆ is poorly sintered, the conventional LaB ₆ target produced by sintering a commercial powder has only a relative density of about 80% and contains a large amount of voids. In this cavity, organic components, moisture, and the like are usually adsorbed. This organic component or moisture is released into the vacuum chamber during sputtering, contaminating the chamber, or introduced into the sputtering film, causing a problem of degrading the performance of the film. In order to suppress the influence of the public, in the case of the LaB ₆ sputter target, it is preferable that the relative density of not less than 88%.

As a method of densifying a sintered compact, there exists a method of adding a sintering adjuvant to lanthanum boride powder and performing sintering (for example, refer patent document 1 and 2). In this case, since metal oxide is usually used as a sintering aid, the metal oxide remains as impurities in the sintered body even after sintering. When this sintered compact is used as a target material, there exists a problem that the impurity in a sintered compact is introduce | transduced into a sputtering film, and causes the performance of a film to fall.

On the other hand, as a sputtering target using a metal boride, it is a sputtering target whose main component is one or more selected from hafnium boride, titanium boride, tungsten boride, and lanthanum boride, and the sintered compact density ratio of the said target is 80% or more, and also The target for sputtering whose crystal grain diameter is 50 micrometers or less, and its manufacturing method are disclosed (for example, refer patent document 3).

This technique makes a high density boride target by greatly reducing the space | gap between the particle | grains of a target, and improving the relative density of the said target. However, this technique is a technique for improving the mass productivity of the product produced using this target, and there is no mention at all about the high purity of a target.

Japanese Patent Laid-Open No. 61-261272 Japanese Patent Laid-Open No. 4-228474 Japanese Unexamined Patent Publication No. 6-248446

MEANS TO SOLVE THE PROBLEM The present inventors conducted the research about the effective manufacturing method of the high purity, high density (high-density) metal boride sintered compact which is suitable as a constituent material of the target for sputtering, and the lanthanum boride sintered compact which can obtain a lanthanum boride thin film with a small work function. . As a result, the present inventors have found that the method of sintering lanthanum boride powder washed in an inorganic acid is effective in order to obtain lanthanum boride sintered compact with high purity.

Specifically, when the metal boride powder is washed with an inorganic acid, the metal oxide, boron oxide, and metal-boron complex oxide contained as impurity oxides are dissolved in the inorganic acid, but the metal carbides and boron carbides contained as impurity carbides Insoluble in inorganic acids. The present inventors have found that by heating a metal boride powder to a specific temperature in the air, an oxidized impurity carbide is oxidized to an oxide, and the oxide oxidized impurities can be removed by acid cleaning the powder subjected to the oxidation treatment.

However, in the LaB ₆ sputtering film formed using the target which consists of a highly purified LaB ₆ sintered compact obtained by the said technique, the applicable board | substrate is limited and the sputter | spatter obtained when the physical property of a film forming board | substrate and LaB ₆ differs greatly as mentioned above. The properties of the membrane were not sufficient.

The present invention has been made under such a situation, and a LaB ₆ sintered body suitable as a sputtering target for producing a LaB ₆ thin film having high purity, high density, excellent crystallinity, and good work function, a target using the same, and the target are used. It is an object of the present invention to provide an lanthanum hexaboride film formed by forming a film and an effective method for producing the LaB ₆ sintered body.

As described above, in general, when a film having a composition or crystal structure different from that of a film forming substrate is formed by sputtering, an internal stress is generated in the sputter film due to the difference in physical properties of the film and the film, resulting in poor crystallinity of the film. Peeling occurs.

The present inventors, by employing the (固溶) to the other elements in the sintered body for a target, variations occur in the LaB ₆ crystal lattice, and by the deformation target is to relieve the internal stress at the time of sputtering film formation, intensive studies As a result, it was found that the internal stress of the sputtered film can be alleviated by dissolving nitrogen in the LaB ₆ sintered body.

In addition, unlike an impurity to increase the work function of the LaB ₆ present as a mixture of the LaB _6, the nitrogen is employed in a grid of sintered LaB _6. By using the LaB ₆ sintered compact in which such nitrogen solution was dissolved as a target, the LaB ₆ sputtered film which nitrogen solution dissolved was formed into a film. Is by sputtering the nitrogen content of the LaB ₆ sintered for nitrogen capacity is not necessarily consistent with the nitrogen capacity of the LaB ₆ sintered body for a target, but the target in the film in a range from 0.1 mass% to 3.0 mass% LaB ₆ sputter film crystalline It was found to be high.

In addition, while the content of nitrogen is in the above range, the content of impurities composed of at least two elements selected from carbon single particles and / or La, C, O and B is 0.3 vol% or less. The LaB ₆ sintered compact has been found to be suitable as a sputtering target for producing a LaB ₆ thin film having high purity, a relative density of 88% or more, excellent crystallinity, and good work function.

This LaB ₆ sintered compact can be manufactured effectively by performing a specific process using LaB ₆ powder as a raw material.

This invention is completed based on this knowledge.

That is, the present invention,

[1] The nitrogen element content is 0.1% by mass or more and 3% by mass or less, and the content of impurities composed of at least two elements selected from carbon alone and / or La, C, O and B is 0.3 vol% or less, A lanthanum tetraborate sintered compact, wherein the relative density of the sintered compact is 88% or more,

[2] the lanthanum tetraborate sintered body according to [1], wherein the carbon content is less than 0.1% by mass and the oxygen content is less than 1.0% by mass,

[3] the lanthanum hexaboride sintered body according to [1] or [2], wherein the lattice constant is 4.1570 GPa or more and 4.1750 GPa or less;

[4] a target using the lanthanum hexaboride sintered compact according to any one of [1] to [3],

[5] a lanthanum hexaboride film having a work function of 3.1 eV or less formed by sputtering a target according to [4], by ultraviolet photoelectron spectroscopy,

[6] (a) Heat treatment of lanthanum hexaboride powder at temperature of 600 ° C or higher and 800 ° C or lower in air, (b) Acid treatment of heat treated product of lanthanum hexaboride powder obtained in step (a) And a step of (c) sintering the acid treated product of the lanthanum hexaboride powder obtained in the step (b) under a gas atmosphere of nitrogen at a temperature of 1800 ° C. or higher and a pressure of 30 MPa or higher. In the step), the oxygen content in the acid treated product of the obtained lanthanum hexaboride powder is adjusted to less than 1.0 mass%, and the carbon content is adjusted to less than 0.1 mass%, to any one of [1] to [3]. The manufacturing method of the lanthanum 6 boron sintered compact described,

[7] The acid treated product of the lanthanum hexaboride powder after the step (b) has an average particle diameter of 1 µm or more and 5 µm or less, and further (b ') between the steps (b) and (c). As the above step, the acid treated material is mixed with fine lanthanum hexafluoride powder having an average particle diameter of 50 nm or more and 500 nm or less to obtain a mixed powder. In the step (c), the mixed powder is subjected to the above conditions. The manufacturing method of the lanthanum tetraborate sintered compact as described in [6] which sinters,

[8] In the step (b '), the mass M _N of the acid treated product and the mass M _S of the fine lanthanum hexaboride powder have a mass ratio (M _N / M _S ) of 97/3 to 70/30. Method for producing lanthanum tetraboride sintered body as described in [7],

[9] The fine lanthanum hexafluoride powder is used to reduce impurities in the obtained product after thermal reduction treatment of the lanthanum-containing compound and the boron-containing compound at a temperature of 1200 ° C to 1500 ° C in a vacuum or in an inert gas atmosphere. The manufacturing method of the lanthanum tetraborate sintered compact as described in [7] or [8] which was processed,

[10] The method for producing a lanthanum hexaboride sintered body according to any one of [7] to [9], wherein the lanthanum hexaboride sintered body is a sintered body for a target;

To provide.

According to the present invention, a LaB ₆ sintered body suitable as a sputtering target or the like for producing a LaB ₆ thin film having high purity, compactness, excellent crystallinity and good work function, a target formed using the same, and a film formed by using the target It is possible to provide an lanthanum hexaboride film and an effective method for producing the LaB ₆ sintered body.

1 is an SEM photograph of a LaB ₆ sintered body of Example 1. FIG.
2 is a SEM photograph of a LaB ₆ sintered body of Comparative Example 3. FIG.

First, the LaB ₆ sintered compact of this invention is demonstrated.

[LaB ₆ sintered body]

LaB ₆ sintered body of the present invention has a nitrogen element content of 0.1% by mass or more and 3% by mass or less, and the content of impurities composed of at least two kinds of elements selected from carbon alone and / or La, C, O and B is 0.3. As a volume% or less, the relative density of a sintered compact is 88% or more, It is characterized by the above-mentioned.

(Solution of nitrogen element into LaB ₆ sintered lattice)

In general, when a film having a composition or crystal structure different from that of a film forming substrate is formed by sputtering, an internal stress is generated in the sputtered film due to a difference in physical properties of the substrate and the film, resulting in poor crystallinity of the film, resulting in peeling of the film. Problems occur.

In order to cope with such a problem, the LaB ₆ sintered body of the present invention has a solid solution of nitrogen in the LaB ₆ crystal lattice of the sintered body, relieves internal stress in the sputtered film, and improves crystallinity. The content of the nitrogen element in the LaB ₆ sintered body of the present invention, requires that 0.1 mass% to 3.0 mass% or less. If the nitrogen content is less than 0.1% by mass, the deformation of the LaB ₆ crystal lattice is small and the film internal stress caused by the difference in physical properties between the film forming substrate and the LaB ₆ film cannot be sufficiently relaxed, so that the crystallinity of the LaB ₆ sputtered film is not improved. Further, the nitrogen content is more than 3 mass%, LaB ₆ modifications may be reducing film becomes large over the internal stress in the crystal lattice, it deteriorates the LaB ₆ film is sputter crystallinity. From such a viewpoint, it is preferable that content of the said nitrogen element is 0.1 mass% or more and 2.0 mass% or less, and it is more preferable that they are 0.2 mass% or more and 1.0 mass% or less.

The nitrogen element is an element belonging to group 15 of the periodic table (long form). 15 other than the nitrogen element group element (P, As, Sb, Bi ) is a LaB ₆ Even if not employed or employed, the same results as those employed with nitrogen are not obtained. The reason is that, since the other 15 elements are van der waals radius is significantly sizes other than the nitrogen atom, when the Group 15 element other than nitrogen element exists, LaB ₆ is too large, variation of the crystal lattice, film-forming substrate and a LaB ₆ film It is considered that the stress in the film generated by the characteristic difference cannot be relaxed. On the other hand, nitrogen having a small van der waals radius is relatively simply dissolved in the crystal lattice of LaB ₆ .

In addition, group 15 elements, since the work function of the size compared with the LaB _6, the group 15 elements that can not be employed the greater the work function, and if present in the LaB ₆ film. However, it was found that a small amount of nitrogen element has little effect on the work function of LaB ₆ because the crystal structure does not change significantly.

Therefore, by dissolving nitrogen, the internal stress of the sputtered film can be alleviated without affecting the work function.

In addition, when nitrogen is dissolved in the LaB ₆ sintered body, it basically becomes an invasive solid solution in which nitrogen invades the atomic gap of the LaB ₆ crystal lattice. In the case of forming an invasive solid solution, the lattice constant becomes large compared with the solid solution. Therefore, by evaluating the lattice constant of the LaB ₆ sintered compact by XRD (X-ray diffraction method), it can be confirmed that the nitrogen element is dissolved in the lattice of the LaB ₆ sintered compact.

Nitrogen element content and the LaB case between the lattice constant of the sintered body ₆ is not necessarily that a constant relationship is established, the art is the content of nitrogen element at least 0.1% by weight 3% by mass or less, more than the lattice constant of 4.1570Å LaB ₆ sintered 4.1750Å Limiting to the following is preferable at the point which can obtain the sputter film excellent in crystallinity. If less than 1 mass%, the content of the nitrogen element, since the lattice constant is equal 4.1590Å less, more crystallinity is obtained LaB ₆ film is good sputtering, is more preferable.

In addition, the nitrogen element content in the sintered body is LaB _6, into the pulverized sintered body in a graphite crucible and heated in a He gas and melting in the combustion tube can be confirmed by measuring the nitrogen in the generated gas by a thermally conductive projection.

For the method of employing the nitrogen element in the lattice of the LaB ₆ sintered body will be described in detail the method of manufacturing a LaB ₆ sintered body of the present invention described below.

(impurities)

The LaB ₆ sintered body of the present invention requires that the content of impurities composed of carbon alone and / or at least two elements selected from La, C, O and B be 0.3 vol% or less.

Wherein the impurity content exceeds 0.3% by volume, it is much the impurity content in the target obtained with the art LaB ₆ sintered body. As a result, impurities are also introduced into the sputtered film, whereby a LaB ₆ film having high purity and excellent crystallinity cannot be obtained. Preferable impurity content is 0.2 volume% or less, More preferably, it is 0.1 volume% or less.

Further, the impurity content is, the value observed by a SEM, calculated from the area ratio on the impurities in the field of view of the art LaB ₆ sintered body. The size of one field of view was 720 micrometers x 940 micrometers, and the observation value of 20 fields was summed and the said area ratio was calculated | required.

The impurity content in the art LaB ₆ sintered body, LaB ₆ can be expressed as the oxygen content and carbon content in the sintered body, the oxygen content is preferably less than 1.0% by mass, and more preferably not more than 0.5% by mass and carbon Preferably content is less than 0.1 mass%, More preferably, it is 0.05 mass% or less.

In addition, oxygen content and carbon content based on the said impurity are the values measured by the method shown below.

First, a LaB ₆ sintered compact sample is used as a crushed powder, and it is set as a measurement sample. The oxygen content is a method of heating a measurement sample in a graphite crucible in an inert gas atmosphere, reacting oxygen decomposed or dissociated from the measurement sample with carbon, and quantifying the generated carbon monoxide or carbon dioxide by infrared absorbance, that is, usually an inert gas melting method. It measures by the method called.

In addition, carbon content heats a measurement sample in a quartz tube furnace, and measures the carbon component generated by volatilization, decomposition, combustion, etc. from a measurement sample using an infrared absorption method.

As said impurity, 1 type (s) or 2 or more types chosen from a carbon single body, a lanthanum carbide, a boron carbide, a lanthanum oxide, a boron oxide, and a lanthanum-boron complex oxide are mentioned, for example.

To the content of impurities other than the nitrogen element in the art LaB ₆ sintered product to below 0.3% by volume, it is preferable to carry out the high purity process for removing impurities contained in the raw material powder of the LaB _6. This high purity treatment is explained in detail in the method for producing a LaB ₆ sintered body of the present invention described later.

Here, in the case where nitrogen is dissolved in the LaB ₆ sintered body, the presence of lanthanum nitride in which lanthanum and nitrogen are dissolved in an amorphous state can be considered, in addition to the invasive solid solution in which nitrogen has invaded the atomic gap of the LaB ₆ crystal lattice. However, the lanthanum nitride, LaB ₆ in that it has the potential to ease the internal stress of the sputtering film, a nitrogen and the compound is not and is within a range of the impurity.

As described above, the LaB ₆ sintered compact requires that the nitrogen element content is 0.1% by mass or more and 3% by mass or less and the impurity content other than the nitrogen element is 0.3% by volume or less, and the sintered body relative density is 88% or more. If the relative density is less than 88%, since a large amount of pores are contained in the target obtained using the LaB ₆ sintered body, the organic component adsorbed in the pores, moisture, and the like are released into the vacuum chamber during sputtering, The inside is contaminated or introduced into the sputtering film, which causes a decrease in the performance of the sputtering film.

In addition, the said relative density refers to the density ratio of the actual sintered compact with respect to theoretical density.

Next is a description of the production method of the LaB ₆ sintered body of the present invention.

[Method for producing LaB ₆ sintered body]

Method of manufacturing a LaB _6, the sintered body of the present invention, (a) LaB step of heat-treating the ₆ powder, at a temperature of less than 600 ℃ 800 ℃ in the air, (b) heating of the LaB ₆ powder obtained in the step (a) A step of acid-treating the processed material, and (c) a step of sintering the acid-treated product of LaB ₆ powder obtained in the step (b) at a temperature of 1800 ° C. or higher and a pressure of 30 MPa or more in a nitrogen gas atmosphere, Further, in the step (b), the oxygen content in the acid treated product of the obtained LaB ₆ powder is adjusted to less than 1.0 mass%, and the carbon content is adjusted to less than 0.1 mass%.

In the production method of the LaB ₆ sintered body of the present invention, to the content of impurities other than the nitrogen element in the LaB ₆ sintered body obtained by more than 0.3% by volume, a high purity treatment of LaB ₆ powder used as a raw material is carried out.

(High Purification Treatment of Raw Material LaB ₆ Powder)

In the manufacturing method of this invention, the said (a) process and (b) process are implemented as a high purity treatment. The detail of these (a) process and (b) process is as follows.

<(a) process>

In the art high purity processing (a) step is a step that the atmosphere of the raw material powder, LaB _6, the heat treatment at a temperature of less than 600 ℃ 800 ℃.

LaB ₆ of the raw material powder is, and may be used to synthesized, may be used a commercially available product. These LaB ₆ powders contain one or two or more impurities selected from among carbon alone, lanthanum oxide, lanthanum carbide, boron oxide, lanthanum boron composite oxide, and boron carbide which are unavoidably incorporated at the time of manufacture. In the production method of the present invention, first, the heat treatment in the atmosphere of the raw material powder, LaB _6, and converts the lanthanum carbide and boron carbide, the respective oxides. The lanthanum oxide, boron oxide, and lanthanum boron composite oxide can be easily removed by the (b) acid treatment step of the next step. In addition, carbon single substance is removed as carbon dioxide by this process.

In the manufacturing method of this invention, the oxidation treatment temperature in air | atmosphere is 600 degreeC or more and 800 degrees C or less. The reason is that the carbon alone, the lanthanum carbide and the boron carbide are not sufficiently oxidized below 600 ° C, and when it exceeds 800 ° C, LaB ₆ itself is oxidized and the yield decreases.

The average particle diameter of the used LaB ₆ powder is preferably 0.1 µm or more and 20 µm or less, more preferably 0.5 µm or more and 10 µm or less, more preferably 1 from the viewpoint of the sinterability in the (c) sintering step described later. It is more than 5 micrometers. If the average particle diameter is 0.1 µm or more, the removal of oxygen and carbon is easy, and the production cost is also low. If the average particle diameter is 20 µm or less, the surface energy serving as the driving force for sintering becomes large and it is easy to obtain a high density sintered body.

<(b) process>

In the art of high purity process (b) step is a step of acid treatment for a heat treatment of the LaB ₆ powder product obtained from the (a) step.

The inorganic acid for eluting the oxidized impurity in the said (b) process can be chosen from hydrochloric acid, sulfuric acid, and nitric acid. Here, it is preferable to select the kind, density | concentration, processing temperature, and processing time of the inorganic acid to be used according to the component and content of the oxide to melt | dissolve. This is because when the oxidizing power of the inorganic acid is too high, not only the oxide but also LaB ₆ itself is oxidized and dissolved, and the yield of LaB ₆ itself decreases. On the other hand, when the oxide dissolving power of the inorganic acid is low, it is time to dissolve the oxide. This is because, in some cases, dissolution becomes insufficient and the oxide cannot be sufficiently removed. Although inorganic acids include phosphoric acid and hydrofluoric acid, phosphoric acid lacks solubility, hydrofluoric acid has strong solubility, LaB ₆ itself also dissolves, and it is a poison and has a high risk and is not a suitable inorganic acid. On the other hand, organic acids are inadequate because they lack oxide dissolving power.

Since nitric acid and sulfuric acid have strong oxidizing power, there is a high possibility of oxidizing and dissolving LaB ₆ itself, and it is necessary to exercise caution in selecting and controlling treatment conditions strictly. On the other hand, since hydrochloric acid has little oxidation power, it is unlikely to oxidize and dissolve LaB ₆ itself and can be suitably used.

For example, when using hydrochloric acid, the concentration is at least 1 mol / dm ^{3 and} more preferably at most 6 mol / dm ³ . The reason for this is that the elution rate of impurities is slower than 1 mol / dm ³ , and it takes time. When it exceeds ₆ mol / dm ³ , LaB ₆ itself is easily oxidized. More preferable concentration is 2 mol / dm ³ or more and 6 mol / dm ³ or less, and particularly preferable concentration is 4 mol / dm ³ or more and 6 mol / dm ³ or less.

Moreover, although this process may be performed at normal temperature, it is preferable to carry out by heating. The processing temperature in the case of heat processing is 40 degreeC or more, and 80 degrees C or less is preferable. This is because elution of impurities takes time below 40 ° C., and LaB ₆ itself is easily oxidized when it exceeds 80 ° C.

The powder after the acid treatment is preferably dried, particularly vacuum dried, in order to remove water after removing the acid component with pure water or ion-exchanged water. The reason for vacuum drying is to avoid reacting with LaB ₆ to produce oxidizing impurities when the water evaporates.

In this way, high purity processing on the raw material LaB ₆ powder ((a) step and the (b) step) that by carrying out, preferably the oxygen content of the acid treated in the LaB ₆ powder obtained is less than 1.0% by mass, more preferably Preferably it is less than 0.5 mass%, and also adjusts carbon content to less than 0.1 mass%, More preferably, less than 0.05 mass%.

<(b ') process>

Between the step (b) and the step (c) described later, as the step (b '), a LaB ₆ powder subjected to a high purity treatment comprising the step (a) and the step (b) (of the LaB ₆ powder the acid treatment may be water), it makes the process of obtaining the mixed powder was mixed with the art LaB the average particle diameter is smaller than _6, LaB ₆ fine powder powder.

In addition, in description concerning this (b ') process, the said LaB ₆ powder which performed the said high-purification process may be called LaB ₆ powder N, and this fine LaB ₆ powder may be called fine LaB ₆ powder S.

In this way, two kinds of lanthanum hexaboride powders having different average particle diameters are mixed, and the mixed powder is molded and sintered in the step (c) described later to produce a high purity and high density lanthanum hexaboride sintered body.

(LaB ₆ Powder N)

In the case of using in the step (b '), the average particle diameter of LaB ₆ powder N is preferably 1 µm or more and 5 µm or less from the viewpoint of making it larger than fine LaB ₆ powder S. The average particle diameter of this LaB ₆ powder N becomes like this. More preferably, they are 1 micrometer or more and 4 micrometers or less, More preferably, they are 1 micrometer or more and 3 micrometers or less.

In addition, since the particle size reduction rate when the LaB ₆ powder of the raw material is LaB ₆ powder N by the above-mentioned high purity treatment is only about several%, the average of the LaB ₆ powder of the raw material instead of prescribing the average particle diameter of the LaB ₆ powder N Even if the particle size is defined in the above range, there is no substantial difference.

(Fine LaB ₆ Powder S)

Since the fine LaB ₆ powder S has a smaller average particle diameter than the LaB ₆ powder N described above, the surface area is large and the surface energy serving as a driving force for sintering is large, so the particles themselves are excellent in sinterability. However, since the particle size is small, the particles are formed unevenly due to the strong van der Waals force, and the filling properties of the particles are deteriorated. As a result, there is a problem that the contact between the particles becomes insufficient, and the sintering reaction is difficult to start.

The present inventors, the fine LaB ₆ powder S than the average particle diameter is large, charging property is excellent LaB ₆ powder N of the fine and the LaB ₆ powder S was added an appropriate amount if the contact of the particles be taken sufficiently large in the art fine LaB ₆ powder S It was found that excellent sinterability is exhibited by surface energy.

Art LaB ₆ fine powder S is preferably not more than 500㎚ or more, the average particle diameter 50㎚. When this average particle diameter is less than 50 nm, it is difficult to manufacture a large quantity and it is not economical. Moreover, when an average particle diameter is larger than 500 nm, the effect of improving the relative density of a lanthanum boride sintered compact is not seen. This average particle diameter becomes like this. More preferably, they are 50 nm or more and 300 nm or less, More preferably, they are 60 nm or more and 200 nm or less.

But are not limited to the production method of such fine powder LaB ₆ S, followed by shattering of the powder that is commercially available LaB ₆ as a jet mill, a bead mill or the like may be adjusted in a predetermined particle size.

Moreover, you may synthesize | combine by a hydrothermal synthesis method by adding heat reduction synthesis | combination, synthesis | combination with a thermal plasma, or a reducing agent in a reducing atmosphere of a lanthanum compound and boron carbide. Moreover, you may grind these obtained powders by jet mill, bead mill, etc., and may adjust to predetermined particle diameter.

As a preferable manufacturing method of the fine LaB ₆ powder S, after a heat reduction process of a lanthanum containing compound and a boron containing compound in the vacuum or inert gas atmosphere at the temperature of 1200 degreeC or more and 1500 degrees C or less, containing the obtained lanthanum boride The method of performing the process which reduces the impurity in a product is mentioned.

Here, the treatment for reducing impurities can be carried out by various methods, and the method is not limited. Examples thereof include acid cleaning and the like using a mixture of an inorganic acid and water. As an inorganic acid used for acid washing, hydrochloric acid is preferable in order to suppress oxidation of the obtained lanthanum boride. The product obtained by the heat reduction process contains many impurities other than lanthanum boride as a raw material group. By performing the process which reduces the impurity by acid washing, for example, carbon content in a product can be 2.0 mass% or less, and oxygen content can be 3.0 mass% or less.

In addition, the same high purity treatment as that for obtaining LaB ₆ powder N described above, that is, the heat treatment in the step (a) and the acid treatment in the step (b) are carried out, and the impurity content is about the same as that of a commercial product. for example, the carbon content is 0.5 mass% or less, and more preferable that the oxygen content to less than 1.0% by mass, when the impurity content of the same order as the above-mentioned powder LaB ₆ N, more preferred.

In addition, the average particle diameter of the said LaB ₆ powder N and the fine LaB ₆ powder S is the value measured by the scanning electron microscope (SEM).

In addition, these carbon content and oxygen content are the values measured by the said infrared absorption method and inert gas melting method.

(Mixing ratio of LaB ₆ powder N and fine LaB ₆ powder S, and mixing method)

In the production method of the present invention, the mass M _S of the mass of the LaB ₆ fine powder N M _N and LaB ₆ S powder, preferably a mass ratio (mass M _N / M _S wt) 97/3 to 70/30, more Preferably it mixes in the ratio of 96/4-90/10. With respect to the total amount of LaB ₆ powder N and fine LaB ₆ powder S, when the content of the fine LaB ₆ powder S is less than 3% by mass, since the addition amount is insufficient when the large surface energy of the fine LaB ₆ powder S contributes, the relative density The effect of improvement may not be obtained. When more than 30 mass%, under the influence of the aggregation of the fine LaB ₆ powder S, filling property may fall and a sintering reaction may become difficult to occur. In addition, greater than 30% by mass, even if avoiding agglomeration in any way, it is not practical in view of production cost of the LaB ₆ fine powder S. In addition, since the fine LaB ₆ powder S has a large surface area and a lot of oxygen content derived from the surface oxide layer, when the addition amount of the fine LaB ₆ powder S is too large, the oxygen content contained in the sintered body increases, and when used as a target material, sputtering In some cases, the performance of the film may be reduced.

Various methods can be taken about a mixing method, The method is not limited, For example, the method of slurrying in an organic solvent and performing ball mill mixing etc. is mentioned. Moreover, you may add an arbitrary binder, slurry into an organic solvent, and perform ball mill mixing.

It is preferable to dry the mixed powder under reduced pressure or in an inert atmosphere. Moreover, you may dry and dry it by spray-drying etc. and it may be set as granule.

<(c) process>

This step (c) uses an acid treated product of LaB ₆ powder obtained by the above-mentioned step (b) or a mixed powder of LaB ₆ powder N and fine LaB ₆ powder S obtained by the step (b '), In a nitrogen gas atmosphere, a compact LaB ₆ sintered compact is obtained by sintering on the temperature of 1800 degreeC or more and the pressure of 30 Mpa or more, and a nitrogen element is solid-dissolved in the lattice of the obtained LaB ₆ sintered compact.

In this sintering step, the LaB ₆ powder obtained by the high-purification treatment may be molded and sintered as it is, or may be added in a solvent with an optional binder to slurry, and may be molded and degreased after granulation.

In general, LaB ₆ powder is poorly sinterable, but by pressing and sintering the highly purified LaB ₆ powder at 1800 ° C. or higher and press pressure 30 MPa or higher in nitrogen gas, the nitrogen content is 0.1% by mass to 3% by mass or less and impurities other than nitrogen. A LaB ₆ sintered body having a content of 0.3% by volume or less and a relative density of 88% or more can be obtained.

It is suitable to perform pressure sintering using a hot press apparatus. The obtained LaB ₆ powder is filled into the graphite mold in the hot press apparatus and pressure-sintered in nitrogen gas at about 1800 degreeC or more and about 1950 degrees C or less, press pressure 30 MPa or more, and about 40 MPa or less. Thereby, the sintered compact whose impurity content is 0.3 volume% or less, nitrogen content is 0.1 mass% or more and 3 mass% or less, and whose relative density is 88% or more can be obtained.

If it is less than 1800 degreeC, since the temperature required for densification is insufficient, the sintered compact which has a relative density of 88% or more cannot be obtained even if it increases the amount of pressurization, and when it exceeds 1950 degreeC, particle growth is promoted, and there exists a possibility that a relative density may fall.

Moreover, when the pressure is less than 30 MPa, sufficient densification is not performed and a sintered compact whose relative density is 88% or more cannot be obtained. The higher the pressure, the better, but the internal pressure of the sintering jig usually used for hot press sintering is 40 MPa, and since there is almost no high pressure-resistant jig thereon, the upper limit is 40 MPa as a reference.

As another method of dissolving nitrogen, there is a method of heat treating LaB ₆ powder before sintering in nitrogen. This heating temperature requires 1000 degreeC or more. When the heating temperature is increased to sufficiently solidify the nitrogen, the sintering activity is lowered due to grain growth, and thus, it is necessary to grind again. In this case, it is unavoidable that impurities are contained in the LaB ₆ powder by oxidation by grinding. Therefore, sintering in a nitrogen atmosphere is preferable as a method of dissolving nitrogen.

Moreover, if conditions are provided, you may use another sintering method, such as a hot isotropic press (HIP) sintering method.

These by the manufacturing method of the LaB ₆ sintered body of the present invention, a high purity and, and dense, crystallinity can be excellent, and also a work function of manufacturing a LaB ₆ sintered body is suitable as a sputtering target, such as the preferred LaB ₆ thin film for producing, efficiently.

[Target and LaB ₆ Sputter Film]

The invention also, by sputtering with the above-mentioned properties (性狀) target, characterized in that using a LaB ₆ sintered body of the present invention and, the target also provides a LaB ₆ film formed of a sputter.

By sputtering using a target using LaB ₆ having a low impurity content and appropriately controlling nitrogen content, a LaB ₆ sputtered film having high purity and excellent crystallinity can be obtained as compared with the case of using a conventional LaB ₆ target.

That is, in order to form a LaB ₆ sputtered film excellent in crystallinity and high purity, it is a LaB ₆ sintered compact used for a target, It has a relative density of 88% or more, Nitrogen content is 0.1 mass% or more and 3 mass% or less, and nitrogen The other impurity content of 0.3 volume% or less is used. The LaB ₆ sintered body preferably has an oxygen content based on impurities of less than 1.0% by mass, more preferably 0.5% by mass or less, preferably carbon content of less than 0.1% by mass, and more preferably 0.05% by mass. It is as follows.

The LaB ₆ sputtered film obtained in this way with high purity and excellent crystallinity has a small work function. The work function of the LaB ₆ sputtered film is preferably 3.1 eV or less, more preferably 2.8 eV or less, and still more preferably 2.7 eV or less.

Examples of the measurement of the work function include Kelvin probe methods in addition to photoelectron spectroscopy such as ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). Although the photoelectron spectroscopy has high measurement accuracy, the apparatus is expensive and the measurement cost is high. On the other hand, the Kelvin probe method is inexpensive because the device is inexpensive, and the measurement cost is low, but the measurement accuracy is slightly inferior. Therefore, in this invention, the measured value by ultraviolet photoelectron spectroscopy (UPS) is used as a value of a work function among the photoelectron spectroscopy, and the value of the work function measured by the Kelvin probe method is used as a reference.

As the sputtering equipment, but generally it includes a two-pole DC glow discharge sputtering apparatus, a magnetron sputtering apparatus, an ion beam sputtering apparatus, a target using a LaB ₆ sintered body of the present invention can be applied to any sputtering apparatus.

It is preferable that the atmosphere at the time of sputtering is inert gas atmosphere, such as Ar gas.

The material of the object (substrate or the like) of LaB ₆ film-forming sputter film is not particularly limited, but includes, for example, a synthetic resin such as a metal such as tungsten, copper, glass, Si wafer, and a polyamide resin. It is preferable that the temperature at the time of sputtering is 0 degreeC or more and 300 degrees C or less. The higher the temperature at the time of sputtering, the LaB ₆ sputtered film having excellent crystallinity is obtained, but if it is 300 ° C or higher, there is a possibility that the thermal stress in the case of cooling to room temperature after film formation may be excessive and a substrate is introduced into the sputter chamber. This is because it takes time until the substrate temperature becomes uniform and productivity is insufficient.

The upper limit of the sputtering temperature is determined by the film forming substrate. For example, there is no problem when sputtering on a substrate having heat resistance such as a metal or Si wafer, but when sputtering on a resin substrate, it is necessary to form the film below the heat resistance temperature of the resin. Therefore, in order to apply more generally, it is preferable to form into a film below 100 degreeC.

On the other hand, when the temperature at the time of sputtering is 0 degrees C or less, since cooling other than water is needed in order to cool the temperature in a sputter chamber, it is unpreferable. Therefore, the temperature at the time of sputtering becomes like this. Preferably it is 0 degreeC or more and 300 degrees C or less, More preferably, it is 0 degreeC or more and 100 degrees C or less.

Example

Next, although an Example demonstrates this invention still in detail, this invention is not limited at all by these examples.

In addition, all the characteristics in each case were measured by the following method.

In addition, the average particle diameter of various powders was measured by the scanning electron microscope (SEM) (The Hitachi, Ltd. make, S-4000). The longest diameter was measured about 300-500 particle | grains for every various powder, and the average was made into the average particle diameter.

<High Purification LaB ₆ Powder>

(1) Measurement of oxygen content and carbon content

Oxygen content took 50 mg of sample powders, and measured it by the said inert gas melting method using the oxygen-nitrogen simultaneous analyzer (LE-4 make, TC-436).

Moreover, carbon content took 100 mg of sample powders, and measured by the method using the said infrared absorption using the carbon analyzer (WC-200 by LECO company).

<Fine LaB ₆ Powder>

(2) Measurement of oxygen content and carbon content

In the same manner as the high purity process LaB ₆ powder was measured oxygen content and the carbon content.

<Sintered body of LaB ₆ powder>

(3) oxygen content and carbon content

After the sintered compact sample was crushed minutes, in the same manner as in the LaB ₆ powder it was measured oxygen content and the carbon content.

(4) impurity content

About the sintered compact sample which became crushed powder, it observed with the scanning electron microscope (SEM) (Hitachi make, S-4000), and calculated | required impurity content from the area ratio of the impurity phase in the visual field. In addition, the size of one field of view was 720 micrometers x 940 micrometers, and the observation value of 20 fields was summed and the said area ratio was calculated | required.

(5) Identification of impurity species

Elemental analysis was performed using an electron probe microanalyzer (EPMA: JXA-8800, manufactured by Nihon Electronics Co., Ltd.) for the impurity image in the SEM observation field.

(6) relative density

Density is calculated using the so-called Archimedes method, which measures the weight in air and the weight in water of a sintered compact sample using commercially available electronic balance, and calculates the density from the obtained buoyancy value, and the density ratio to the theoretical density (relative density) ) Was obtained.

(7) content of nitrogen element

Nitrogen content of the sintered compact took 50 mg of sample powder, and measured it by the said thermal conductivity method using the oxygen-nitrogen simultaneous analysis apparatus (The product made by LECO, TC-436).

(8) Confirmation of nitrogen element solid solution into lattice of LaB ₆ sintered body

Using an X-ray diffraction apparatus (PANalytical X'Pert PRO, manufactured by Spectris Co., Ltd.), lattice constants were calculated using peaks of 400, 410, 411, 331, 420, and 421 planes of LaB ₆ , by comparing the theoretical value, within the lattice of the LaB ₆ sintered body was found to have a nitrogen element are employed.

<LaB ₆ sputter film>

(9) Measurement of work function by vacuum UPS method

Using an ultraviolet photoelectron spectrometer (MUL-010HI, manufactured by PHI), the work function of the LaB ₆ sputtered film was measured at a pressure of 1.33 × 10 ⁻⁶ Pa.

(10) Measurement of work function by Kelvin probe method

Using a Kelvin probe (Scan Kelvin Probe SKP5050, manufactured by KP Technology), the work function of the LaB ₆ sputtered film was measured in air.

(11) thin film XRD measurement

The X-ray diffraction measurement was performed using the thin film X-ray diffraction apparatus (PW3040 / 00 by Nippon-Philips company). As an X-ray source, the measurement angle (2θ) was set to 20 to 100 degrees using CuKα rays (wavelength lambda; 0.154 nm). From the obtained result, the peak intensity was compared for each sputtered film with respect to the peak of the crystal plane with the strongest intensity.

Example 1

(1) High Purification Treatment of LaB ₆ Commercially Available Powder

The LaB ₆ commercial powder was subjected to oxidation treatment at 700 ° C. in air, followed by acid treatment at 60 ° C. in 6 mol / dm ³ hydrochloric acid. The powder after acid treatment was washed with ion-exchanged water until the pH of the filtrate became 6 or more and the chlorine ion concentration became 1 mg / dm ³ or less, and vacuum dried at 110 ° C. Obtained LaB ₆ powder had an oxygen content of 0.38 mass% and a carbon content of 0.006 mass% based on impurities. Moreover, the average particle diameter of the obtained LaB ₆ powder was 1.5 micrometers.

(2) Preparation of LaB ₆ Sintered Body

The LaB ₆ powder subjected to the high purity treatment in (1) was sintered at 1950 ° C. at 40 MPa for 2 hours in a nitrogen gas with a hot press. The obtained sintered compact had a relative density of 92.4%, and nitrogen content was 0.44 mass%, and impurity content other than nitrogen comprised from amorphous boron carbide and an amorphous lanthanum-boron composite oxide was 0.006 volume%. The impurity content was 0.21 mass% in carbon content and 0.011 mass%. In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1578Å, was compared to the theoretical value increases the lattice constant. This confirmed that the nitrogen element was dissolved in the lattice of the LaB ₆ sintered compact.

(3) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in (2) above, in using a magnetron sputtering apparatus, Ar gas was subjected to the sputtering film forming pressure to 0.5Pa, temperature 20 ℃. The obtained LaB ₆ film contains almost no impurities other than nitrogen, and compared with the case where a LaB ₆ sintered compact in which the nitrogen element of Comparative Example 1 described later is not dissolved is used for the target, the peak intensity by thin film XRD measurement was about 2.5. The crystallinity was high. The work function was 3.6 eV in the Kelvin probe method.

Treatment conditions and results are shown in the first table.

Example 2

(1) High Purification Treatment of LaB ₆ Commercially Available Powder

It is the same as Example 1 (1).

(2) Preparation of LaB ₆ Sintered Body

The powder subjected to the high purity treatment in the above (1) was sintered at 1950 ° C. at a press pressure of 30 MPa for 2 hours in a nitrogen gas with a hot press device. The obtained sintered compact has a relative density of 91.5%, the nitrogen content is 0.42 mass%, the impurity content other than nitrogen which consists of amorphous boron carbide and an amorphous lanthanum boron composite oxide is 0.008 volume%, and the impurity content is carbon content It was 0.25 mass% in 0.015 mass% and oxygen content. In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1576Å, was compared to the theoretical value increases the lattice constant. This confirmed that the nitrogen element was dissolved in the lattice of the LaB ₆ sintered compact.

(3) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in (2) above, in using a magnetron sputtering apparatus, Ar gas was subjected to the sputtering film forming pressure to 0.5Pa, temperature 20 ℃. The obtained LaB ₆ film contains almost no impurities other than nitrogen, and compared with the case where a LaB ₆ sintered compact in which the nitrogen element of Comparative Example 1 described later is not dissolved is used for the target, the peak intensity by thin film XRD measurement was about 2.0. The crystallinity was high. The work function was 3.6 eV in the Kelvin probe method and 2.6 eV in the vacuum UPS method, and had a smaller value in comparison with Comparative Example 1.

Treatment conditions and results are shown in the first table.

Example 3

(1) High Purification Treatment of LaB ₆ Commercially Available Powder

It is the same as Example 1 (1).

(2) Preparation of LaB ₆ Sintered Body

The LaB ₆ powder subjected to the high purity treatment in (1) was sintered at 1950 ° C. at 40 MPa for 3 hours in a nitrogen gas with a hot press. The obtained sintered compact had a relative density of 91.7%, and nitrogen content was 0.99 mass%, and impurity content other than the nitrogen element comprised from amorphous boron carbide and an amorphous lanthanum-boron composite oxide was 0.005 volume%. The impurity content was 0.018 mass% in carbon content, and 0.18 mass% in oxygen content. In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1581Å, was compared to the theoretical value increases the lattice constant. This confirmed that the nitrogen element was dissolved in the lattice of the LaB ₆ sintered compact.

(3) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in (2) above, in using a magnetron sputtering apparatus, Ar gas was subjected to the sputtering film forming pressure to 0.5Pa, temperature 20 ℃. The obtained LaB ₆ film contains almost no impurities other than nitrogen and has a peak intensity of about 1.7 by thin film XRD as compared with the case where the target uses a LaB ₆ sintered compact in which the nitrogen element of Comparative Example 1 described later is not dissolved in the target. The crystallinity was high. The work function was 3.7 eV in the Kelvin probe method.

Treatment conditions and results are shown in the first table.

Example 4

(1) High Purification Treatment of LaB ₆ Commercially Available Powder

It is the same as Example 1 (1).

(2) Preparation of LaB ₆ Sintered Body

The powder subjected to the high purity treatment in the above (1) was sintered for 6 hours at 1950 ° C. and a press pressure of 40 MPa in a nitrogen gas with a hot press. The obtained sintered compact had a relative density of 89.5%, and nitrogen element content was 2.9 mass%, and impurity content other than nitrogen comprised from amorphous boron carbide and an amorphous lanthanum boron composite oxide was 0.01 volume%. The impurity content was 0.038 mass% in carbon content, and 0.17 mass% in oxygen content.

In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1736Å, was compared to the theoretical value increases the lattice constant. This confirmed that the nitrogen element was dissolved in the lattice of the LaB ₆ sintered compact.

(3) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in (2) above, in using a magnetron sputtering apparatus, Ar gas was subjected to the sputtering film forming pressure to 0.5Pa, temperature 20 ℃. The obtained LaB ₆ film contains almost no impurities other than nitrogen, and the peak intensity by thin film XRD measurement is about 1.5, compared with the case where the target uses a LaB ₆ sintered compact in which the nitrogen element of Comparative Example 1 described later is not dissolved in the target. The crystallinity was high. The work function was 3.7 eV in the Kelvin probe method.

Treatment conditions and results are shown in the first table.

Example 5

(1) High Purification Treatment of LaB ₆ Commercially Available Powder

It is the same as Example 1 (1).

(2) Preparation of LaB ₆ Sintered Body

The LaB ₆ powder subjected to the high purity treatment in (1) was sintered at 1800 ° C. at 40 MPa for 2 hours in a nitrogen gas with a hot press. The obtained sintered compact had a relative density of 90.8%, and nitrogen element content was 0.28 mass%, and impurity content other than nitrogen comprised from amorphous boron carbide and an amorphous lanthanum-boron composite oxide was 0.005 volume%. The impurity content was 0.23 mass% in carbon content and 0.013 mass%. In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1574Å, was compared to the theoretical value increases the lattice constant. This confirmed that the nitrogen element was dissolved in the lattice of the LaB ₆ sintered compact.

(3) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in the above (2), by using the magnetron sputtering apparatus was performed in an Ar gas, the sputtering film formation pressure to 6.7Pa. The obtained LaB ₆ film contains almost no impurities other than nitrogen elements, and compared with the case where a LaB ₆ sintered body in which the nitrogen element of Comparative Example 1 described later is not dissolved is used for the target, the peak intensity by thin film XRD measurement is weak. 2.0 times, crystallinity was high. The work function was 3.6 eV in the Kelvin probe method.

Treatment conditions and results are shown in the first table.

Example 6

(1) High Purification Treatment of LaB ₆ Commercially Available Powder

It is the same as Example 1 (1).

(2) Preparation of LaB ₆ Sintered Body

The highly purified LaB ₆ powder in (1) was sintered for 2 hours at 1800 ° C. and a press pressure of 30 MPa in a nitrogen gas with a hot press. The obtained sintered compact had a relative density of 89.6%, and nitrogen content was 0.15 mass%, and impurity content other than the nitrogen element comprised from amorphous boron carbide and an amorphous lanthanum-boron composite oxide was 0.009 volume%. The impurity content was 0.25 mass% in carbon content and 0.015 mass% in oxygen content. In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1573Å, was compared to the theoretical value increases the lattice constant. This confirmed that the nitrogen element was dissolved in the lattice of the LaB ₆ sintered compact.

(3) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in the above (2), by using the magnetron sputtering apparatus was performed in an Ar gas, the sputtering film formation pressure to 6.7Pa. The obtained LaB ₆ film contains almost no impurities other than nitrogen elements, and compared with the case where a LaB ₆ sintered body in which the nitrogen element of Comparative Example 1 described later is not dissolved is used for the target, the peak intensity by thin film XRD measurement is weak. 1.5 times, crystallinity was high. The work function was 3.7 eV in the Kelvin probe method and 3.0 eV in the vacuum UPS method, and had a small value as compared with Comparative Example 1.

Treatment conditions and results are shown in the first table.

Example 7

(1) High Purification Treatment of LaB ₆ Commercially Available Powder

It is the same as Example 1 (1).

(2) Preparation of LaB ₆ Sintered Body

5 mass% of LaB ₆ microparticles (average particle diameter: 100 nm, oxygen content 0.7 mass%, carbon content 0.1 mass%) is added to LaB ₆ powder of the average particle diameter 1.5 micrometers obtained by the high-purity treatment in said (1), and hot It sintered at 1800 degreeC and press pressure of 30 Mpa in nitrogen gas by the press apparatus for 2 hours. The obtained sintered compact had a relative density of 94.3%, and nitrogen element content was 0.33 mass%, and impurity content other than the nitrogen element comprised from amorphous boron carbide and an amorphous lanthanum boron composite oxide was 0.007 volume%. The impurity content was 0.024 mass% in carbon content, and 0.20 mass% in oxygen content. In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1576Å, was compared to the theoretical value increases the lattice constant. This confirmed that the nitrogen element was dissolved in the lattice of the LaB ₆ sintered compact.

(3) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in (2) above, in using a magnetron sputtering apparatus, Ar gas was subjected to the sputtering film forming pressure to 0.5Pa, temperature 20 ℃. The obtained LaB ₆ film contains almost no impurities other than nitrogen elements, and compared with the case where a LaB ₆ sintered body in which the nitrogen element of Comparative Example 1 described later is not dissolved is used for the target, the peak intensity by thin film XRD measurement is weak. 2.6 times, crystallinity was high. In addition, the work function was 3.5 eV in the evaluation by the Kelvin probe method.

Treatment conditions and results are shown in the first table.

Example 8

(1) High Purification Treatment of LaB ₆ Commercially Available Powder

It is the same as Example 1 (1).

(2) Preparation of LaB ₆ Sintered Body

5 mass% of LaB ₆ microparticles similar to Example 7 were added to the LaB ₆ powder of the average particle diameter 1.5 micrometers obtained by carrying out the high-purity treatment in said (1), and it is 1950 degreeC in nitrogen gas by the hot press apparatus, and press pressure is 30 Mpa. Sintered for 2 hours. The obtained sintered compact had a relative density of 96.1%, and the nitrogen content was 0.40 mass%, and impurity content other than the nitrogen element comprised from amorphous boron carbide and an amorphous lanthanum boron composite oxide was 0.011 volume%. The impurity content was 0.031 mass% in oxygen content, and 0.15 mass% in oxygen content. In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1577Å, was compared to the theoretical value increases the lattice constant. This confirmed that the nitrogen element was dissolved in the lattice of the LaB ₆ sintered compact.

(3) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in (2) above, in using a magnetron sputtering apparatus, Ar gas was subjected to the sputtering film forming pressure to 0.5Pa, temperature 20 ℃. The obtained LaB ₆ film contains almost no impurities other than nitrogen elements, and compared with the case where the target uses a LaB ₆ sintered compact in which the nitrogen element of Comparative Example 1 described later is not dissolved in the target, the peak intensity of the thin film XRD measurement is about 2.8. The crystallinity was high. The work function was 3.45 eV in the Kelvin probe method and 2.4 eV in the vacuum UPS method, and had a smaller value in comparison with Comparative Example 1.

Treatment conditions and results are shown in the first table.

Comparative Example 1

(1) High Purification Treatment of LaB ₆ Commercially Available Powder

It is the same as Example 1 (1).

(2) Preparation of LaB ₆ Sintered Body

The LaB ₆ powder subjected to the high purity treatment in (1) was sintered in an argon gas at 1950 ° C. and a press pressure of 40 MPa for 2 hours using a hot press. The obtained sintered compact had a relative density of 89.5%, and nitrogen content was 0.006 mass%, and impurity content other than the nitrogen element comprised from amorphous boron carbide and an amorphous lanthanum-boron composite oxide was 0.005 volume%. The impurity content was 0.35 mass% in carbon content and 0.015 mass% in oxygen content. In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1567Å, it was hardly different from the theoretical value. This confirmed that the nitrogen element was hardly dissolved in the lattice of the LaB ₆ sintered compact.

(3) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in (2) above, in using a magnetron sputtering apparatus, Ar gas was subjected to the sputtering film forming pressure to 0.5Pa, temperature 20 ℃. The obtained LaB ₆ film contains almost no impurities other than the nitrogen element, and compared with the case where the solid-state LaB ₆ sintered body in which the nitrogen element of Example 1 was used was used as the target, the peak intensity of LaB ₆ by the thin film XRD measurement was 40%. To that extent, the crystallinity was low. The work function was 3.9 eV in the Kelvin probe method and 3.7 eV in the vacuum UPS method.

Treatment conditions and results are shown in the first table.

Comparative Example 2

(1) Preparation of LaB ₆ LaB ₆ sintered body using a commercially available powder

The LaB ₆ commercial powder was sintered at 1950 ° C. at 40 MPa for 2 hours in a nitrogen gas with a hot press. The obtained sintered compact had a relative density of 91.5%, and nitrogen content was 0.45 mass%, and impurity content other than the nitrogen element comprised from amorphous boron carbide and an amorphous lanthanum-boron composite oxide was 0.9 volume%. The impurity content was 0.3 mass% in carbon content and 1.8 mass% in oxygen content. In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1576Å, was compared to the theoretical value increases the lattice constant. This confirmed that the nitrogen element was dissolved in the lattice of the LaB ₆ sintered compact.

(2) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in the above (1), by using the magnetron sputtering apparatus was performed in an Ar gas, the sputtering film formation pressure to 6.7Pa. Obtained LaB ₆ film, as compared with the case highly purified and sintered in a nitrogen gas after the process using a target of LaB ₆ sintered body of Example 1 is made, the peak intensity of the LaB ₆ by the thin film XRD measurement, but has the same value, LaB ₆ A large amount of impurities having a crystal structure other than the crystal structure were contained. The work function was 3.8 eV in the Kelvin probe method and 3.2 eV in the vacuum UPS method.

Treatment conditions and results are shown in the first table.

Comparative Example 3

(1) High Purification Treatment of LaB ₆ Commercially Available Powder

It is the same as Example 1 (1).

(2) Preparation of LaB ₆ Sintered Body

The highly purified LaB ₆ powder in (1) was sintered for 2 hours at 1800 ° C. and a press pressure of 20 MPa in a nitrogen gas with a hot press. The obtained sintered compact had a relative density of 86.5%, and nitrogen content was 0.10 mass%, and impurity content other than the nitrogen element comprised from amorphous boron carbide and an amorphous lanthanum-boron composite oxide was 0.08 volume%. The impurity content was 0.020 mass% in carbon content, and 0.33 mass% in oxygen content. In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1571Å, was compared to the theoretical value increases the lattice constant. This confirmed that a small amount of nitrogen element was dissolved in the lattice of the LaB ₆ sintered compact.

(3) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in (2) above, in using a magnetron sputtering apparatus, Ar gas was subjected to the sputtering film forming pressure to 0.5Pa, temperature 20 ℃. The obtained LaB ₆ film contains almost no impurities other than the nitrogen element, and compared with the case where the target was a LaB ₆ sintered body in which the nitrogen element of Example 1 was dissolved in an appropriate range, the peak of LaB ₆ was measured by thin film XRD. The film had a low crystallinity of about 20%. The work function was 4.8 eV in the Kelvin probe method and 4.2 eV in the vacuum UPS method.

Treatment conditions and results are shown in the first table.

Comparative Example 4

(1) High Purification Treatment of LaB ₆ Commercially Available Powder

It is the same as Example 1 (1).

(2) Preparation of LaB ₆ Sintered Body

The highly purified LaB ₆ powder in (1) was sintered for 6 hours at 1950 ° C. and a press pressure of 20 MPa in a nitrogen gas with a hot press. The obtained sintered compact had a relative density of 87.5%, and nitrogen content was 3.5 mass%, and impurity content other than the nitrogen element comprised from amorphous boron carbide and an amorphous lanthanum-boron composite oxide was 0.2 volume%. The impurity content was 0.042 mass% in oxygen content, and 0.11 mass% in oxygen content. In addition, the lattice constant of the obtained sintered body is LaB ₆ 4.1759Å, was compared to the theoretical value increases the lattice constant. This confirmed that the nitrogen element was dissolved in the lattice of the LaB ₆ sintered compact.

(3) Sputtering film forming which targets LaB ₆ sintered compact

By targeting the LaB ₆ sintered body obtained in (2) above, in using a magnetron sputtering apparatus, Ar gas was subjected to the sputtering film forming pressure to 0.5Pa, temperature 20 ℃. The obtained LaB ₆ film contains almost no impurities other than nitrogen elements, and compared with the case where the LaB ₆ sintered compact of Comparative Example 1 was used as a target, the peak intensity of LaB _{6 in} the thin film XRD measurement was about 90% lower in crystallinity. It was. The work function was 4.0 eV in the Kelvin probe method.

Treatment conditions and results are shown in the first table.

[State]

(1) In Examples 1 to 8, Comparative Example 1 and Comparative Example 3, the oxygen content based on the impurity, which is obtained by subjecting LaB ₆ commercially available powder to high purity treatment as a raw material of the sintered body, is 0.38% by mass and the carbon content is The thing of 0.006 mass% and an average particle diameter of 1.5 micrometers was used.

Embodiments 7,8, was used as a further LaB ₆ fine particles, an oxygen content of 0.7% by weight, a carbon content of 0.1% by mass, the average particle diameter 100㎚.

(2) In Comparative Example 2, commercially available LaB ₆ powder was used as a raw material of the sintered compact. * 1 has a peak intensity equivalent to that of the sputtered film of Example 1, but indicates that a large amount of impurities having a crystal structure other than the LaB ₆ crystal structure were contained in the thin film XRD measurement.

As is apparent from the first table, all of the LaB ₆ sintered bodies of Examples 1 to 8 had nitrogen element content in the range of 0.1 mass% or more and 3 mass% or less, and impurity content other than nitrogen element contained 0.3 volume%. It is less than and relative density is higher than 88%. In addition, the sputtering films of Examples 1 to 8 had a peak intensity ratio in the thin film XRD of about 1.5 times to about 2.5 times as compared to the sputtering film targeted to the LaB ₆ sintered body in which the nitrogen element of Comparative Example 1 was not dissolved. The crystallinity is high below and the work function by the Kelvin probe method is 0.2 to 0.45 eV. In addition, as apparent from Examples 2, 6, 8 and Comparative Examples 1 to 3, the rank of the work function measured by the Kelvin probe method and the rank of the work function measured by the vacuum UPS method are the same. In this respect, it is expected that the work function of the sputtered films of Examples 1 to 8 by the vacuum UPS method is also lower than that of the comparative example 1.

In contrast, since the LaB ₆ sintered compact of Comparative Example 1 is sintered in argon gas, no nitrogen element is dissolved. The sputtering film of Comparative Example 1 had a low peak crystallinity of about 40% of the sputtering film of Example 1, low crystallinity, and high work function by the Kelvin probe method and the vacuum UPS method. Comparative Example 2, except LaB Since accept the ₆ commercially available powder, obtained LaB _6, the sintered body is high as 0.9% by volume content of impurities other than the nitrogen atom, during the sputter film that target the art LaB ₆ sintered body, LaB ₆ It contains a lot of impurities, and the work function by Kelvin probe method and vacuum UPS method is high. In Comparative Example 3, since the sintering pressure was low at 20 MPa, the obtained LaB ₆ sintered body had a low relative density of 86.5% and a work function by the Kelvin probe method and the vacuum UPS method. Comparative Example 4, because of its high as 3.5% by weight of nitrogen element content, a low crystallinity as a sputtering film, about 90% of a sputtering film of Comparative peak intensity ratio in Example 1 to target the art LaB ₆ sintered according to the Kelvin probe method The work function is also high.

In Examples 7, 8, two kinds of particles (LaB ₆ particles and LaB ₆ fine particles) having different average particle diameters are used. Therefore, Examples 7 and 8 are higher in Examples 1 to 6 and Comparative Examples 1 to 4 than the relative density (94.3% and 96.1%) of the LaB _6, the sintered body. In Examples 7 and 8, compared with Examples 1 to 6 and Comparative Examples 1 to 4, the peak intensity ratio (2.6 and 2.8 times) of the LaB ₆ sputtered film was high, so that the crystallinity was high, and the Kelvin probe method was used. Low work function (3.5 and 3.45 eV). In addition, the work function by the vacuum UPS method of Example 8 is 2.4 eV, and is the lowest among Examples 1-8 and Comparative Examples 1-4.

In addition, Example 1 of the SEM photograph of the sintered LaB ₆ also shows a first, Figure 2 shows a SEM picture of the relative density of the sintered LaB _6, the lowest in Comparative Example 3.

Table 2 shows the results of elemental analysis of the LaB ₆ sintered bodies of Examples 1 to 8 and Comparative Examples 1 to 4. In addition, although La, C, O, and B show the value by the said EPMA analysis, about N, it is a value by the result measured by the said thermal conductivity method. As is apparent from Table 2, the impurity was composed of carbon alone and / or at least two elements selected from La, C, O and B.

The LaB ₆ sintered body of the present invention is suitable as a sputtering target for producing a LaB ₆ thin film having high purity, compactness, excellent crystallinity and good work function.

Claims (10)

Nitrogen element content is 0.1 mass% or more and 3 mass% or less, and the content of the impurity comprised from carbon single-piece | unit and / or at least 2 sort (s) of element chosen from La, C, O, and B is 0.3 volume% or less, and it is relative of a sintered compact. A lanthanum tetraborate sintered compact whose density is 88% or more. The method of claim 1,
The lanthanum tetraborate sintered compact whose carbon content is less than 0.1 mass% and whose oxygen content is less than 1.0 mass%. The method according to claim 1 or 2,
A lanthanum tetraborate sintered compact having a lattice constant of 4.1570 Pa or more and 4.1750 Pa or less. The lanthanum-hexaboride sintered compact as described in any one of Claims 1-3 was used. The target characterized by the above-mentioned. The lanthanum hexaboride film whose work function by ultraviolet photoelectron spectroscopy which formed into a film by sputtering the target of Claim 4 is 3.1 eV or less. (a) heat-treating the lanthanum hexaboride powder at a temperature of 600 ° C. or higher and 800 ° C. or lower in the air; (b) acid treating the heat treated product of lanthanum hexaborate powder obtained in step (a); and (c) a step of sintering the acid treated product of the lanthanum hexaboride powder obtained in the step (b) under a nitrogen gas atmosphere at a temperature of 1800 ° C. or higher and a pressure of 30 MPa or higher, and further comprising the step (b). WHEREIN: The oxygen content in the acid treated material of the lanthanum hexaboride powder obtained is adjusted to less than 1.0 mass%, and carbon content is adjusted to less than 0.1 mass%, The 6th term | claim of any one of Claims 1-3 characterized by the above-mentioned. Method for producing lanthanum boride sintered body. The method according to claim 6,
The acid treated material of the lanthanum hexaboride powder after the step (b) has an average particle diameter of 1 µm or more and 5 µm or less,
Between the steps (b) and (c), as the step (b '), the acid treated product is mixed with fine lanthanum hexaboride powder having an average particle diameter of 50 nm or more and 500 nm or less to obtain a mixed powder. Has a process,
The said (c) process WHEREIN: The manufacturing method of the lanthanum 6 boron sintered compact which sinters the said mixed powder on the said conditions. The method of claim 7, wherein
In the step (b '), the mass M _N of the acid treated product and the mass M _S of the fine lanthanum hexaboride powder are mixed at a ratio of 97/3 to 70/30 by mass ratio (M _N / M _S ). The manufacturing method of a lanthanum 6 boride sintered compact. 9. The method according to claim 7 or 8,
The fine lanthanum hexafluoride powder is subjected to a treatment for reducing impurities in the obtained product after the heat reduction treatment of the lanthanum-containing compound and the boron-containing compound at a temperature of 1200 ° C or more and 1500 ° C or less in a vacuum or an inert gas atmosphere. The manufacturing method of a lanthanum 6 boron sintered compact. 10. The method according to any one of claims 7 to 9,
The manufacturing method of the lanthanum 6 boron sintered compact whose lanthanum hexasulfide sintered compact is a sintered compact for targets.

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